1. Field of the Invention
The present invention relates to a method of manufacturing a structure by using a film forming technology, and specifically, to a method of manufacturing a structure by using a spray deposition method. Furthermore, the present invention relates to a structure manufactured by using such a manufacturing method.
2. Description of a Related Art
Conventionally, as a technology of forming a thin film or thick film, the sputtering method, sol-gel method, vapor deposition method, thermal spray method, aerosol deposition (AD) method, etc. are known. Among them, especially, the AD method receives attention as a technology that enables forming a strong thick film by employing a hard and brittle material such as ceramic.
The AD method is a method of depositing raw material powder by generating an aerosol containing the raw material powder and spraying it from the nozzle toward a substrate, and also referred to as gas deposition method, spray deposition method, or fine particle beam deposition method. In the AD method, a film is formed by the mechanochemical reaction in which the raw material powder sprayed at high speed impinges on and cuts into an under layer, that is, the substrate or the previously formed under layer of the deposited material, and a crushed surface produced by the crushing of the powder at the time of impingement adheres to the under layer. Therefore, according to the AD method, a dense and strong thick film containing no impurity can be formed. The phenomenon that the raw material powder cuts into the under layer is referred to as “anchoring”.
Such AD method is suitable for the case of fabricating a brittle material (hard and brittle material) including ceramic. According to the AD method, a laminated structure including plural material layers such as a multi-layer capacitor can be fabricated easily. Further, a film of PZT (Pb (lead) zirconate titanate) as a kind of ceramic, formed on the substrate by using the AD method is applied as a piezoelectric actuator, a piezoelectric pump, an ink-jet printer head, and an ultrasonic transducer.
In the AD method, since the collision energy generated when the material powder impinges on the under layer is utilized to deposit the material on the under layer, at the time of film formation, generally, a substrate having hardness of some degree such as silicon, glass, sapphire, or SUS (special use steel) is used.
Further, Japanese Patent Application Publication JP-A-2003-34003 discloses a method of forming a brittle material structure on a resin base material without cutting the resin base material. In this method, after a foundation layer of a hard material is formed on the surface of the resin substrate, the brittle material is allowed to impinge on the foundation layer by using the fine particle beam deposition method such that a part of the brittle material cuts into the foundation layer to form an anchor part. Thereby, a polycrystalline brittle structure is formed in which there is substantially no crystalline orientation and no grain boundary made of a glass layer at the boundary of the crystals. According to the method, by using the AD method, a structure can be formed also on a resin substrate.
By the way, since a structure formed on a substrate by using a film forming technology such as the AD method is strongly in close contact with the substrate, it is difficult to separate the substrate therefrom. Accordingly, such a structure is often utilized with a substrate attached thereto. However, it is not negligible that the existence of the substrate causes deterioration of the function of the structure or the device using the structure.
For example, in an ultrasonic transducer fabricated by using the substrate as described above, the propagation efficiency of ultrasonic waves is deteriorated by the substrate. Accordingly, it is conceivable that the substrate is removed from the structure by grinding or the like. However, grinding of the substrate is difficult, and sometimes the structure is damaged by the stress at the time of grinding. On the other hand, in the case of trying to remove the substrate by chemical etching, the film stress concentrated on the boundary between the AD film and the substrate is released and cracking occurs on the back surface of the AD film by the reaction, which results in deterioration in yield. Therefore, a method is desired that enables easy removal of a substrate from a structure.
Furthermore, Japanese Patent Application Publication JP-A-2003-215256 discloses that, in a method of manufacturing a radiation detector assembly, a phosphor layer having a filling factor of 5% to 40% is formed by using the gas deposition method. However, this manufacturing method is objected to make the sensitivity and the sharpness of the radiation detector assembly higher, and the easy removal of the substrate from the structure is not disclosed therein.